Igniter for air bag system

ABSTRACT

The present invention provides an igniter for an air bag system which has an excellent operation performance and can be reduced in weight.  
     A capacitor and an integrated circuit are provided in an igniter for an air bag system utilizing bus lines  10  and  11.  In the integrated circuit, an impedance converting circuit is provided between the bus lines  10  and  11  and a rectifying circuit, and thereby, a capacitor with a large capacitance (μF order) can be charged with a small load capacitance (pF order).

TECHNICAL FIELD TO WHICH THE INVENTION BELONGS

[0001] The present invention relates to an igniter for an air bag systemused in an air bag system utilizing a bus system, an integrated circuitfor an air bag system, and a method for charging a capacitor provided inan igniter for an air bag system.

PRIOR ART

[0002] An air bag system for protecting a passenger from an impact at atime of collision of a vehicle is indispensable, and the air bag systemneeds to be reduced in weight from a demand for reducing weight of awhole vehicle. Recently, kinds and the total number of air bags such asan air bag for a driver side, an air bag for a passenger side next tothe driver, an air bag for a rear seat side, and an air bag for an sideimpact are increasing, and therefore, a lighter air bag system is ingreater demand.

[0003] In a current air bag system, an electronic control unit (ECU)connected to a power source (a battery in a vehicle) and an impactdetecting sensor are individually connected to individual gas generators(a gas generator and an air bag are accommodated in a module case). Anaspect of the connection between the ECU and the individual gasgenerators is shown in FIG. 11.

[0004] As shown in FIG. 11, the ECU and an igniter (FIG. 12) of each ofthe individual gas generators are necessarily connected to each otherthrough two conductors, and thereby, conductors double the number of thetotal number of igniters are required. Having many conductorscontributes largely to weight increase in an air bag system. In view ofconstraints at a time of assembling vehicle parts, the ECU and theindividual gas generators are not connected by only the conductors butconnected by connecting plural conductors via plural connectors, andthereby, there occurs a serious problem such as a weight increase due touse of the connectors and a cost increase due to increase of the numberof the connectors. Further, increase in volume (weight) of the ECU dueto increase in volume of a capacitor incorporated into the ECU as abackup power source for activating all the igniters (serving at a timeof a failure in line between the power source and the ECU) is anotherserious problem.

[0005] In view of the above, a trial for reducing a conductor weightrequired for connection between the ECU and the individual gasgenerators by utilizing a bus system in the air bag system has beenexamined. An aspect of the air bag system utilizing this bus system isshown in FIG. 1.

[0006] As shown in FIG. 1, an air bag system is constituted by providingbus lines comprising plural loop wires passing through the ECU andconnecting each of the individual gas generators to the bus line throughtwo conductors (three or more conductors when occasion demands). In acase of such an air bag system as shown in FIG. 1, since only gasgenerators required corresponding to a collision situation of a vehicleare activated, an integrated circuit receiving information transmissionfrom the ECU and a capacitor supplying a current for activating anigniter are provided in each of the individual gas generators. In thecase of utilizing a bus system, the total number of capacitors isincreased, but since the capacitors are distributed and arranged in theECU and the respective igniters, the capacitance and weight of thecapacitor per igniter is reduced. As a result, since the weight of thecapacitors in this case is remarkably reduced as compared with theweight of the capacitors for backup in the air bag system shown in FIG.11, a large weight reduction is achieved as the whole system in additionto largely reducing the amount of use of conductor, which is expected tobe put in a practical use in the air bag system. Incidentally, therehave been known JP2000-241098A, JP2000-513799A and Japanese Patent No.2707250 as the prior art utilizing the bus system.

DISCLOSURE OF THE INVENTION

[0007] An object of the present invention is to provide an integratedcircuit for an air bag system which achieves a large weight reduction inan entire air bag system by introducing a bus system into the air bagsystem, and which can ensure reliability and rapidness of operationsimilar to those in a conventional art, and which can obtain a highreliability, and an operation control method of an air bag systemutilizing the same.

[0008] According to Automotive Safety Restraint Bus SpecificationVersion 1.0 (Dec. 3, 2001 Philips electronics N. V, TRW Inc., DelphiElectronics Systems, Autoliv Inc., Special Devices Inc.,), a loadcapacity (a load capacity of a capacitor) of an initiator (Slave)corresponding to a bus system is defined to be 250 pF or less. Such acapacitor with a small capacity fails to heat a heat generating portionof an igniter securely at a time of system operation. Therefore, inorder to improve the reliability at a time of an activation time of theigniter, it becomes necessary to use a capacitor with a capacitanceexceeding 250 pF (hereinafter, a capacitance exceeding 250 pF is called“μF order”). However, when a capacitor with a capacitance of the μForder is used, such an abnormality of communication in the bus line isanticipated that most of a current flowing in a bus system (a bus line)is consumed for charging the capacitor so that a current necessary todevelop other required functions can not be supplied.

[0009] In view of the above, the inventors of the present invention havefound that a load capacity of an igniter viewed from a bus line can bemade smaller than an actual load capacity thereof, namely, an igniterhaving a capacitor with an electrostatic capacitance of μF order can bemade to a state that the igniter has a capacitor with a capacitance ofpF order, by providing a circuit for converting an impedance of acharging circuit for charging the capacitor with a current flowing in abus line and supplying a current from the bus line via the circuit, andhas completed the present invention.

[0010] (1) First Solving Means

[0011] An invention described in claim 1 provides, as one means forsolving the above problem, an igniter for an air bag system, which isone or at least two igniters incorporated in the plural of the gasgenerators and used in an air bag system comprising an electroniccontrol unit connected to a power source and an impact detecting sensor,and plural module cases which are connected to the electronic controlunit and accommodate plural gas generators and plural air bags, wherein,

[0012] in the air bag system, a bus line comprising plural loop wireswhich pass through the electronic control unit is provided to supply andtransmit currents and required information, and individual gasgenerators accommodated in the plural module cases are connectedoperationally by plural conductors branched at predetermined portionsfrom the bus line,

[0013] the one or at least two igniters incorporated in the gasgenerator is each electric igniter which is provided with a heatgenerating portion and a priming coming in contact with the heatgenerating portion to ignite the priming by heat generation of the heatgenerating portion due to an ignition current, and the igniter and thebus line are connected to each other through plural conductors, and

[0014] a capacitor and an integrated circuit recorded with informationfor developing a required function are provided in the igniter, acharging circuit for charging a current for igniting the priming in thecapacitor is provided and a circuit for converting an impedance of thecharging circuit is provided between the bus circuit and the capacitor.

[0015] By providing the circuit for converting an impedance of thecharging circuit and performing a current supply to the capacitor fromthe bus line via the circuit for converting an impedance, a capacitorwith a large capacitance (μF order) can be charged with a small loadcapacitance (pF order), so that a current flowing in the bus line isutilized for charging of the capacitor and development of the anotherrequired function.

[0016] In the circuit for converting an impedance, it is preferable touse a MOS-FET or the like as a transistor which can use an emitterfollower circuit including a transistor, and the transistor may beprovided inside or outside the integrated circuit.

[0017] The capacitor can be provided inside or outside the integratedcircuit, and its capacitance is preferably 250 pF to 24 μF, morepreferably 250 pF to 12 μF, and further preferably 250 pF to 6 μF.

[0018] In the above invention, preferably, among the currents from thebus circuit for charging the capacitor and the required information, arectifying circuit having a function for rectifying an alternatingcurrent to make the current flow into the capacitor as a direct currentis provided between the bus circuit and the capacitor, and the circuitfor converting an impedance is provided in a path between the bus lineand the rectifying circuit.

[0019] In the above invention, preferably, among the currents from thebus circuit for charging the capacitor and the required information, arectifying circuit having a function for rectifying an alternatingcurrent to make the current flow into the capacitor as a direct currentis provided between the bus circuit and the capacitor, and the circuitfor converting an impedance is provided between the rectifying circuitand the capacitor.

[0020] Among the currents from the bus circuit for charging thecapacitor and the required information, the rectifying circuit is, forcharging the capacitor, a circuit having a function for rectifying acurrent to flow into a capacitor to be charged and it is preferable thata function for amplifying at least one of a rectified voltage forcharging a capacitor and a voltage applied to the bus line exists in therectifying circuit.

[0021] In the above invention, it is preferable, in view ofsimplification of the entire system, that the impedance convertingcircuit is provided in the integrated circuit.

[0022] In the above invention, it is preferable that the impedanceconverting circuit has a function for controlling an upper limit of acurrent value. By giving such a function to the impedance convertingcircuit, when the capacitor is charged by a current (for example, 10 mA)from the bus line, an instantaneous large current flows in the chargingcircuit, and thereby, a normal current flow in the bus circuit isprevented from being influenced.

[0023] In the above invention, it is preferable that the integratedcircuit has a circuit having a function for detecting abnormality of theheat generating portion of the igniter in the gas generator, a circuithaving a function for identifying each of the plural gas generators, anda circuit having a function for detecting a malfunction of thecapacitor.

[0024] A basic function of the integrated circuit is to receive a signalfrom the ECU in response to a situation occurring when a vehicle hascollided and to activate a gas generator for properly protecting apassenger. In addition thereto, by providing the various functionsdescribed above, quality check of a product at a time of shipping andworkability at a time of assembling are properly improved, and safety atan actual use (while driving a vehicle) and the like can be alsoproperly improved.

[0025] In the above invention, it is preferable that a circuit (noisecountermeasure circuit) for preventing the igniter from being activatederroneously due to noises made outside the igniter is further provided.

[0026] In the above invention, it is preferable that a dischargingwaveform converting circuit for converting a signal waveform of acurrent for igniting the priming stored in the capacitor for eachigniter is further provided, and it is preferable that the dischargingwaveform converting circuit exists in the integrated circuit.

[0027] (2) Second Solving Means

[0028] The invention described in claim 12 provides, as one means forsolving the above problem, an integrated circuit for an air bag systemwhich is provided in one or at least two igniters incorporated into theplural gas generators and used in an air bag system comprising anelectronic control unit connected to a power source and an impactdetecting sensor, and plural module cases which are connected to theelectronic control unit and accommodate the plural gas generators andplural air bags, wherein

[0029] in the air bag system, a bus line comprising plural loop wireswhich pass through the electronic control unit is provided to supply andtransmit currents and required information, and individual gasgenerators accommodated in the plural module cases are connectedoperationally by plural conductors branched at predetermined portionsfrom the bus line,

[0030] the one or at least two igniters incorporated in the gasgenerator is each electric igniter which is provided with a heatgenerating portion and a priming coming in contact with the heatgenerating portion to ignite the priming by heat generation of the heatgenerating portion due to an ignition current, and the igniter and thebus line are connected to each other through plural conductors, and acapacitor and the integrated circuit are provided in the igniter, and

[0031] the integrated circuit is recorded with information fordeveloping a required function, a charging circuit for storing a currentfor igniting a priming in the capacitor is provided, and a circuit forconverting an impedance of the charging circuit is further providedbetween the bus line and the capacitor.

[0032] By providing the circuit for converting an impedance of thecharging circuit and performing current supply to the capacitor from thebus line via the circuit for converting an impedance, a capacitor with alarge capacitance (μF order) can be charged with a small loadcapacitance (pF order), so that a current flowing in the bus line isutilized for charging of the capacitor and development of the anotherrequired function.

[0033] The circuit for converting an impedance can use a transistor, aMOS-FET or the like, and it can be provided inside or outside theintegrated circuit.

[0034] The capacitor can be provided inside or outside the integratedcircuit, and its capacitance is preferably 250 pF to 24 μF, morepreferably 250 pF to 12 μF, and further preferably 250 pF to 6 μF.

[0035] In the above invention, preferably, among the currents from thebus circuit for charging the capacitor and the required information, arectifying circuit having a function for rectifying an alternatingcurrent to make the current flow into the capacitor as a direct currentis provided between the bus circuit and the capacitor, and the circuitfor converting an impedance is provided in a path between the bus lineand the rectifying circuit.

[0036] In the above invention, preferably, among the currents from thebus circuit for charging the capacitor and the required information, arectifying circuit having a function for rectifying an alternatingcurrent to make the current flow into the capacitor as a direct currentis provided between the bus circuit and the capacitor, and the circuitfor converting an impedance is provided between the rectifying circuitand the capacitor.

[0037] Among the currents from the bus circuit for charging thecapacitor and the required information, the rectifying circuit is, forcharging the capacitor, a circuit having a function for rectifying acurrent to flow into a capacitor to be charged and it is preferable thata function for amplifying at least one of a rectified voltage forcharging a capacitor and a voltage applied to the bus line exists in therectifying circuit.

[0038] In the above invention, it is preferable that the impedanceconverting circuit has a function for controlling an upper limit of acurrent value. By giving such a function to the impedance convertingcircuit, when the capacitor is charged by a current (for example, 10 mA)from the bus line, an instantaneous large current flows in the chargingcircuit, and thereby, a normal current flow in the bus circuit isprevented from being influenced.

[0039] In the above invention, it is preferable that the integratedcircuit has a circuit having a function for detecting abnormality of theheat generating portion of the igniter in the gas generator, a circuithaving a function for identifying each of the plural gas generators, anda circuit having a function for detecting a malfunction of thecapacitor.

[0040] A basic function of the integrated circuit is to receive a signalfrom the ECU in response to a situation occurring when a vehicle hascollided and to activate a gas generator for properly protecting apassenger. In addition thereto, by providing the various functionsdescribed above, quality check of a product at a time of shipping andworkability at a time of assembling are properly improved, and safety atan actual use (while driving a vehicle) and the like can be alsoproperly improved.

[0041] In the above invention, it is preferable that a circuit (noisecountermeasure circuit) for preventing the igniter from being activatederroneously due to noises made outside the igniter is further provided.

[0042] In the above invention, it is preferable that a dischargingwaveform converting circuit for converting a signal waveform of acurrent for igniting the priming stored in the capacitor for eachigniter is further provided, and it is preferable that the dischargingwaveform converting circuit exists in the integrated circuit.

[0043] (3) Third Solving Means

[0044] The invention described in claim 22 provides, as one means forsolving the above problem, a method for charging a capacitor provided inan igniter for an air bag system which is provided in one or at leasttwo igniters incorporated into the plural gas generators and used in anair bag system comprising an electronic control unit connected to apower source and an impact detecting sensor, and plural module caseswhich are connected to the electronic control unit and accommodate theplural gas generators and plural air bags, wherein

[0045] in the air bag system, a bus line comprising plural loop wireswhich pass through the electronic control unit is provided to supply andtransmit currents and required information, and individual gasgenerators accommodated in the plural module cases are connectedoperationally by plural conductors branched at predetermined portionsfrom the bus line,

[0046] the one or at least two igniters incorporated in the gasgenerator is each electric igniter which is provided with a heatgenerating portion and a priming coming in contact with the heatgenerating portion to ignite the priming by heat generation of the heatgenerating portion due to an ignition current, and the igniter and thebus line are connected to each other through plural conductors, and

[0047] a capacitor and an integrated circuit recorded with informationfor developing a required function are provided in the igniter, acharging circuit for storing a current for igniting the priming in thecapacitor is provided, and a circuit for converting an impedance of thecharging circuit is provided between the bus circuit and the capacitor,and

[0048] a current is supplied from the power source via the bus line tocharge the capacitor via the circuit for converting an impedance.

[0049] By providing the circuit for converting an impedance of thecharging circuit and performing current supply to the capacitor from thebus line via the circuit for converting an impedance, a capacitor with alarge capacitance (μF order) can be charged with a small loadcapacitance (pF order), so that a current flowing in the bus line isutilized for charging of the capacitor and development of the anotherrequired function.

[0050] The circuit for converting an impedance can use a transistor, aMOS-FET or the like, and it can be provided inside or outside theintegrated circuit.

[0051] The capacitor can be provided inside or outside the integratedcircuit, and its capacitance is preferably 250 pF to 24 μF, morepreferably 250 pF to 12 μF, and further preferably 250 pF to 6 μF.

[0052] In the above invention, preferably, among the currents from thebus circuit for charging the capacitor and the required information, arectifying circuit having a function for rectifying an alternatingcurrent to make the current flow into the capacitor as a direct currentis provided between the bus circuit and the capacitor, and the circuitfor converting an impedance is provided in a path between the bus lineand the rectifying circuit.

[0053] In the above invention, preferably, among the currents from thebus circuit for charging the capacitor and the required information, arectifying circuit having a function for rectifying an alternatingcurrent to make the current flow into the capacitor as a direct currentis provided between the bus circuit and the capacitor, and the circuitfor converting an impedance is provided between the rectifying circuitand the capacitor.

[0054] Among the currents from the bus circuit for charging thecapacitor and the required information, the rectifying circuit is, forcharging the capacitor, a circuit having a function for rectifying acurrent to flow into a capacitor to be charged and it is preferable thata function for amplifying at least one of a rectified voltage forcharging a capacitor and a voltage applied to the bus line exists in therectifying circuit.

[0055] In the above invention, it is preferable, in view ofsimplification of the entire system, that the impedance convertingcircuit is provided in the integrated circuit.

[0056] In the above invention, it is preferable that the impedanceconverting circuit has a function for controlling an upper limit of acurrent value. By giving such a function to the impedance convertingcircuit, when the capacitor is charged by a current (for example, 10 mA)from the bus line, an instantaneous large current flows in the chargingcircuit, and thereby, a normal current flow in the bus circuit isprevented from being influenced.

[0057] In the above invention, it is preferable that the integratedcircuit has a circuit having a function for detecting abnormality of theheat generating portion of the igniter in the gas generator, a circuithaving a function for identifying each of the plural gas generators, anda circuit having a function for detecting a malfunction of thecapacitor.

[0058] A basic function of the integrated circuit is to receive a signalfrom the ECU in response to a situation occurring when a vehicle hascollided and to activate a gas generator for properly protecting apassenger. In addition thereto, by providing the various functionsdescribed above, quality check of a product at a time of shipping andworkability at a time of assembling are properly improved, and safety atan actual use (while driving a vehicle) and the like can be alsoproperly improved.

[0059] In the above invention, it is preferable that a circuit (noisecountermeasure circuit) for preventing the igniter from being activatederroneously due to noises made outside the igniter is further provided.

[0060] In the above invention, it is preferable that a dischargingwaveform converting circuit for converting a signal waveform of acurrent for igniting the priming stored in the capacitor for eachigniter is further provided, and it is preferable that the dischargingwaveform converting circuit exists in the integrated circuit.

[0061] In each invention of the above-described first to third solvingmeans, the number of the loop wires forming the bus line and the numberof the conductors for connecting the bus line and the gas generators maybe two, three, four or more, and the preferable number is two in view ofsimplifying the entire system.

[0062] The priming is not limited to a specific one, but a combinationof a metal or the like and an oxidizing agent such as perchlorate ispreferable, a combination of a metal such as zirconium, titanium, andhafnium and perchlorate is more preferable, and a mixture (ZPP) ofzirconium and potassium perchlorate is particularly preferable.Desirably, the ZPP is formed in particle shape and particle diameters ofzirconium and potassium perchlorate are adjusted.

[0063] In each invention of the above-described first to third solvingmeans, the details of the circuit having the function for detectingabnormality of the heat generating portion of the igniter in the gasgenerator, the circuit having the function for identifying each of theplural gas generators, and the circuit having the function for detectinga malfunction of the capacitor are described in the following items (i)to (iii).

[0064] (i) The circuit having the function for detecting abnormality(failure in line or loose connection between the heat generating portionand the priming, or abnormality of a resistance value of the heatgenerating portion) of the heat generating portion of the igniter in thegas generator:

[0065] As one of conditions required for the gas generator to activatenormally, a contacting state between the heat generating portion of theigniter and the priming has to be good (the heat generating portion andthe priming has to be brought in press-contact with each other). Forexample, when there is a gap between the heat generating portion and thepriming, it is considered that there occurs a malfunction such that thepriming is not ignited when the igniter is actuated or an ignition isdelayed. Further, when the heat generating portion is disconnected orhave been half-disconnected, a similar malfunction occurs. For thisreason, by recording information for detecting the malfunction in theintegrated circuit, an inferior product can be removed at a time ofshipping, and by detecting abnormality at a practical use (while drivinga vehicle), a prompt exchange can be performed.

[0066] Detecting theory for abnormality of the heat generating portion(Thermal Transient Test; issued on pages 461 to 478 in “Progress ofInternational Pyrotechnic Semina” on July 1980 by A. C. Munger) is asfollows: when contacting state of a heat generating portion and apriming is good, an equivalent amount of heat to the heat generated byflowing of a constant current is conducted to the priming, so that thetemperature of the heat generating portion does not rise so high. On theother hand, when the contacting state of the heat generating portion andthe priming is bad, transfer of heat is less, so that the temperaturerising of the heat generating portion becomes higher than a normal case.Therefore, a malfunction is detected by detecting a temperature changedue to such a difference in contacting state as a resistance valuechange and utilizing a temperature coefficient of metal resistance[r=r0(1+αΔT)] to obtain the temperature of the heat generating portion.More specifically, after a resistance r is measured when a current iwhich is too weak to raise the temperature up to igniting the igniter, aresistance R is measured when a current I of 10 to 15 times of thecurrent i is flowed (the temperature of the heat generating portionbecomes about 50 to 100° C., but the priming is not ignited with such atemperature), so that the resistance change due to the temperaturechange of the heat generating portion is obtained as a voltage changewith comparisons of I and i and of R and r. Thus, such measurementinformation is recorded in the integrated circuit.

[0067] (ii) The function for identifying each plurality of gasgenerators:

[0068] For the gas generator for an air bag, various kinds of gasgenerators such as one for a driver side, one for a passenger side nextto the driver, one for a side impact (for a side collision), one for acurtain air bag and the like have been practically used. For example, inthe case of the gas generator for a side impact, the total four gasgenerators are mounted for a driver side, a passenger side next to thedriver, two rear seat sides respectively. For this reason, thoughdifferent information pieces are recorded in the respective integratedcircuits of the gas generators for the driver side, for the passengerside next to the driver, and for two rear seat sides, when theseinformation pieces are recorded at a time of assembling the igniters orthe gas generators or before assembling, since the igniters or the gasgenerators have the same appearance, it is necessary to distinguish thegas generators having the same appearance and having differentinformation pieces recorded or the igniters having the same appearancebefore assembling such that a wrong one is not taken to store andtransport them, which becomes much complicated. Furthermore, with onefor a driver side mounted to a vehicle erroneously as one for apassenger side next to the driver, when activation information of an airbag for a driver side is sent from the ECU, such an erroneous activationthat an air bag for a passenger side next to the driver is inflatedoccurs eventually.

[0069] Therefore, by recording of information for developing identifyingfunction for each plurality of gas generators after assembling of gasgenerators (when differences of gas generators can be recognizedapparently), after gas generators are assembled in module cases (whendifferences of module cases can be recognized apparently) or after gasgenerators are mounted to a vehicle, storage, transportation, managementand the like of gas generators can be made easy, so that a mistake or aconfusion is prevented from occurring at a time of mounting of gasgenerators.

[0070] It is preferable that the information for developing anidentifying function for each plurality of gas generators are recordedafter assembling the gas generators, it is more preferable that theinformation pieces are recorded after the gas generators are assembledin the module cases, and it is further preferable that the informationpieces are recorded after the module cases are mounted to a vehicle.

[0071] (iii) The function for detecting a malfunction of the capacitor:

[0072] The information for developing a function for detecting amalfunction of the capacitor also includes confirmation information of amounted state (soldered state) of a capacitor to a substrate and thelike in addition to information for measuring a pulse response or adielectric dissipation factor.

[0073] After mounted to the vehicle, since the capacitor repeatscharging and discharging, the capacitor deteriorates with age. However,abnormality is detected at a time of a practical use (while driving avehicle) by recording information which can confirm a malfunction due tothis deterioration in the integrated circuit in advance, so that aprompt exchange can be performed. Furthermore, by recording informationfor confirming the soldered state in advance, an inferior product can beremoved at a time of shipping.

[0074] The details of the noise countermeasure circuit in each of theabove-described first to third solving means are as follows:

[0075] For example, when a large current flows at a time of activating acell motor in a vehicle, in case of not providing a noise preventingcircuit, there is a possibility that a noise (a noise causing anuncomfortable unusual sound occurrence while listening to the radio)generated due to this current is transmitted from a vehicle body to flowin an igniter. Due to that the noise is transmitted in this manner, apossibility that an igniter causes an erroneous activation becomes high.Accordingly, by mounting a device constituted to prevent a current fromflowing from a vehicle side to an igniter side, for example, a diode ora varistor (a non-linear resistance element) as the noise countermeasurecircuit (a circuit for preventing an igniter from being activatederroneously), the above-described erroneous activation of the ignitercan be prevented.

[0076] The details of the discharging waveform converting circuit ineach invention of the above-described first to third solving means areas follows:

[0077] The discharging waveform converting circuit has a function forconverting a discharging waveform expressed by the following equation(I) to a triangular wave or a trapezoidal wave:

i(t)=(V0/R)×e ^(−t/CR)   (I)

[0078] (In the equation, v0 represents a capacitor charging voltage (V),R represents a circuit resistance (Ω), C represents a capacitorcapacitance (μF), t represents a time (μsec), and i represents a current(A)). Besides, in order to give a similar converting function, a coilcan be interposed in a connection circuit between the capacitor and theheat generating portion, and the discharging waveform converting circuitcan also be provided in the integrated circuit in view of simplificationof the entire system.

[0079] (4) Other Solving Means

[0080] An invention described in claim 33 provides, as another means forsolving the above-described problem, a gas generator for an air bagwhich comprises, in a housing having a gas discharging port, an igniteractivated by an impact and one or at least two combustion chambersstoring a gas generating agent ignited and burnt by the igniter togenerate a combustion gas for inflating an air bag, wherein as theigniter, the above igniter for an air bag system is provided.

[0081] Furthermore, an invention described in claim 34 provides an airbag system comprising-a gas generator for an air bag, which comprise, ina housing having a gas discharging port, an igniter for an air bagsystem activated by an impact, and one or at least two combustionchambers storing a gas generating agent ignited and burnt by the igniterto generate a combustion gas for inflating an air bag, an impact sensorwhich detects an impact to activate the gas generator, an air bag whichintroduces a gas generated in the gas generator therein to inflate, anda module case which accommodates the air bag therein.

[0082] According to the air bag system employing the present invention,the weight of the entire air bag system can be reduced largely and anoperation performance similar to that in the conventional art can besecured by utilizing the bus system.

BRIEF DESCRIPTION OF THE DRAWINGS

[0083]FIG. 1 is a diagram of an air bag system employing the presentinvention;

[0084]FIG. 2 is an axial sectional view of a gas generator (includingone igniter) used in the air bag system employing the present invention;

[0085]FIG. 3 is an axial sectional view of a gas generator (includingtwo igniters) used in the air bag system employing the presentinvention;

[0086]FIG. 4 is a vertical sectional view of an igniter used in the airbag system employing the present invention;

[0087]FIG. 5 is a vertical sectional view of another embodiment of anigniter used in the air bag system employing the present invention;

[0088]FIG. 6 is a conceptual diagram of an igniter used in the air bagsystem employing the present invention;

[0089]FIG. 7 is a conceptual diagram of an igniter used in the air bagsystem employing the present invention;

[0090]FIG. 8 is a conceptual diagram of an igniter used in the air bagsystem employing the present invention;

[0091]FIG. 9 is a conceptual diagram of an igniter used in the air bagsystem employing the present invention;

[0092]FIG. 10 is a pulse waveform diagram of a bus voltage, a digitaloutput and a charging voltage shown in FIG. 5 to FIG. 9;

[0093]FIG. 11 is a diagram of a conventional air bag system; and

[0094]FIG. 12 is a vertical sectional view of an igniter used in theconventional air bag system.

EXPLANATION OF NUMERALS

[0095]10 and 11 bus line

EMBODIMENT OF THE INVENTION

[0096] An air bag system of the present invention achieves reduction inweight of the entire system by using a bus line and achieves reliabilityof an operation of the system by the above-described solving means.Embodiments including the above-described solving means will beexplained below.

[0097] As shown in FIG. 1, an air bag system employing the presentinvention uses bus lines 10 and 11 comprising two loop wires passingthrough an ECU. The ECU is connected to a power source (a battery in avehicle) and an impact detecting sensor which are not illustrated, and acapacitor for backup, when a conductor connecting the ECU and the powersource is disconnected by an impact at a collision time of a vehicle, isdisposed. Incidentally, in the air bag system employing the presentinvention, since the capacitor is disposed at each of respective gasgenerators (igniters), the capacitor for backup may be one with a smallcapacitance (i.e., light weight), but the capacitor serving for backupin the. conventional air bag system shown in FIG. 11 has to have a largecapacitance in order to activate all the gas generators by itself at atime of failure in line of a lead wire between the battery and the ECU.

[0098] Gas generators in a required number of module cases (which areindicated by black circles. The gas generator and an air bag areaccommodated in the case.) mounted to a vehicle are connected to the buslines 10 and 11 to be actuated, by two conductors (or three or moreconductors when occasion demands).

[0099] As the gas generators in the module cases illustrated with blackcircles in the air bag system shown in FIG. 1, ones shown in FIG. 2 orFIG. 3 can be used according to the number of the igniters. FIG. 2 is anaxial sectional view of a single type gas generator (an igniter 21) inwhich one igniter is provided, and FIG. 3 is an axial sectional view ofa dual type gas generator (igniters 31 and 32) in which two igniters areprovided.

[0100] In the single type gas generator, two (or three or more whenoccasion demands) pins 21 a and 21 b are provided in the igniter 21 andthey are connected to the bus lines 10 and 11 through a connector 25.

[0101] In the dual type gas generator, two (or three or more whenoccasion demands) pins 31 a and 31 b are provided in an igniter 31, two(or three or more when occasion demands) pins 32 a and 32 b are providedin an igniter 32, and the igniters are respectively connected to the buslines 10 and 11 through respective connectors 35 and 36.

[0102] As the igniter 21 and the igniters 31 and 32 in the gasgenerators shown in FIG. 2 and FIG. 3, for example, one shown in FIG. 4or FIG. 5 can be used. FIG. 4 and FIG. 5 show vertical schematicsectional views of igniters, and since igniters having the samestructure can be used as the igniter 21, the igniters 31 and 32, theigniter 21 will be explained below.

[0103] In the igniter 21 shown in FIG. 4, a heat generating portion isprovided on a glass header, an igniting agent (for example, ZPP) ischarged to come in pressure-contact with the heat generating portion,and a substrate provided with a capacitor and an integrated circuit inwhich information for developing required functions has been recorded isdisposed in a lower portion of the igniter 21. The integrated circuit,and the heat generating portion and the capacitor are respectivelyconnected by two conductors, and the integrated circuit is furtherconnected to the pins 21 a and 21 b through conductors.

[0104] In the igniter 21 shown in FIG. 5, a substrate is provided on aglass header, an integrated circuit, in which information for developingrequired functions has been recorded, and a heat generating portion areprovided on one surface of the substrate, and a capacitor (not shown) isprovided on the other surface. The substrate is sealed by insulatingmaterial such as epoxy resin except for the heat generating portion, andonly the heat generating portion comes in contact with a priming.

[0105] The capacitor or the like provided inside of the igniter shown inFIG. 4 or FIG. 5, or the substrate on which the integrated circuit isdisposed may be constituted to have each of structures shown with theconceptual diagrams in FIG. 6 to FIG. 9. FIG. 6 and FIG. 7 show a singleheat generating portion, and FIG. 8 and FIG. 9 show two heat generatingportions. Incidentally, FIG. 10 shows pulse waveforms of a bus voltage,a digital output and a charging voltage shown in FIG. 6 to FIG. 9.

[0106] In FIG. 6 to FIG. 9, a capacitor and an integrated circuitincluding a required circuit are disposed on a substrate, and animpedance converting circuit is provided in a charging circuit from thebus lines 10 and 11 to the capacitor.

[0107] In FIG. 6 and FIG. 8, among the currents from the bus circuit 10and 11 for charging the capacitor and the required information, arectifying circuit having a function for rectifying an alternatingcurrent to make the current flow into the capacitor as a direct currentis provided between the bus circuit 10 and 11 and the capacitor, and theimpedance circuit is provided in a charging circuit from the bus lines10 and 11 to the capacitor via the rectifying circuit.

[0108] In FIG. 7 and FIG. 9, among the currents from the bus circuit 10and 11 for charging the capacitor and the required information, arectifying circuit having a function for rectifying an alternatingcurrent to make the current flow into the capacitor as a direct currentis provided between the bus circuit 10 and 11 and the capacitor, and theimpedance circuit is provided in a charging circuit from the bus lines10 and 11 to the capacitor via the rectifying circuit.

[0109] In FIG. 6 to FIG. 9, a discharging waveform converting circuit(represented with the broken line as “a waveform converter”) can beprovided, if required, and the discharging waveform converting circuititself can be incorporated into the integrated circuit.

[0110] In FIG. 6 to FIG. 9, a switch circuit (a transistor) which shutsoff a current when it is unnecessary to activate an igniter and startssupplying of a current at an activation time of the igniter is provided.When the switch circuit is opened, a current stored in the capacitordoes not flow into the heat generating portion.

[0111] In FIG. 8 and FIG. 9, two heat generating portions share onecapacitor, an integrated circuit in which information for developingrequired functions has been recorded, and a discharging waveformconverting circuit provided if required.

[0112] When the gas generator has two igniters 31, 32, as shown in FIG.3, three operation aspects such that a case of activating only eitherone of the igniters, a case of first activating one of the igniters andthen activating the other with a slight delay, and a case ofsimultaneously activating the two igniters are considered according to acollision state of a vehicle, and, the integrated circuit of the ignitershown in FIG. 8 or FIG. 9 is recorded with such information to make twoheat generating portions generate heat according to each of theabove-described three instruction from the ECU. The igniters 31 and 32of the gas generator shown in FIG. 3 can be made to have the structuresshown in FIG. 6, FIG. 7, or in FIG. 8, FIG. 9.

[0113] The integrated circuits including the capacitor, the impedancecircuit, the rectifying circuit or the like on the substrates shown inFIG. 6 to FIG. 9 are connected to the bus lines 10 and 11 through thepins 21 a and 21 b.

[0114] After a current and information supplied from the bus lines 10and 11 are sent to the integrated circuit, they are converted to digitaloutputs by an A/D converter (an analog/digital converter) to be sent toan MCU (a Micro Computer Unit). Thereafter, an instruction is sent fromthe MCU such that charge control information, position identificationinformation, a failure-detecting information of a heat generatingportion or a resistance value change detecting information is exhibitedand the current is used for charging the capacitor, but it is not usedto make the heat generating portion generate heat.

[0115] A varistor (non-linear resistance element) is disposed in acircuit between the MCU and the heat generating portion as noisepreventing means, and it serves such that the igniter is not activatederroneously due to a noise generated outside the igniter.

[0116] The heat generating portion is put in contact with the priming,and it generates heat by a current supplied only from the capacitor toignite the priming.

[0117] Next, an operation of the air bag system employing the presentinvention will be explained with reference to FIG. 1 to FIG. 9.

[0118] When a vehicle runs normally, failure-detecting information orresistance value change detecting information of the heat generatingportion, detecting information for a malfunction of the capacitor, anddetecting information about whether or not an igniter including anidentifying function required for activating a gas generator (detectinginformation about whether or not an igniter having an identificationfunction for activating a gas generator required for a driver side, apassenger side next to the driver or the like properly at a time ofcollision is disposed rightly, or whether or not another igniter havingthe same identifying function is disposed in a duplicated manner) issent from the ECU to the gas generator (the integrated circuit arrangedin the igniter) through the bus lines 10 and 11 so that whether or notthere is abnormality in these members is checked. When there is anabnormality, an alarm lamp activated in linkage with the air bag system,or the like informs the abnormality, so that an early exchange of partscan be conducted to recover the safety.

[0119] Further, the capacitor of each igniter can be charged from thepower source. At this time, a current supplied from the power sourcethrough the bus lines 10 and 11 is about 10 mA, and an electrostaticcapacitance of the capacitor in the igniter is about μF order. For thisreason, when a current is directly supplied to the capacitor from thebus lines 10 and 11, most of the current is used for charging thecapacitor, so that the above-described each function is not exhibitedsufficiently. However, since the impedance converting circuit isprovided in the charging circuit as shown in FIG. 6 to FIG. 9, acapacitor with a large load capacitance (μF order) can be charged with asmall load capacitance (pF order), so that a current flowing in the buslines 10 and 11 can be utilized not only for charging a capacitor butalso for developing the other required functions.

[0120] When a vehicle provided with the air bag system collides,information from the impact detecting sensor is sent to the ECU, andinformation from ECU is sent, via the bus lines 10 and 11, to a gasgenerator (the integrated circuit provided in the igniter) required toinflate an air bag for ensuring a safety for a vehicle occupant. Bysending a control pulse instructing opening or closing of the switchcircuit from the MCU, the switch circuit is opened or closed.

[0121] If the switch circuit is applied with, for example, a currentpulse with a waveform width of 100 μsec from the MCU, the switch isclosed for 100 μsec and it allows a current from the capacitor to flowin the heat generating portion of the igniter as a pulse with a width of100 μsec. That is, the switch circuit closes a switch while a current (acontrol pulse) is flowing in the switch circuit like a case of using athyristor, a MOS-FET, or a bipolar transistor as the switch circuit. Inthis manner, by applying a pulse with a predetermined time width (20 to500 μsec) to the heat generating portion of the igniter, the heatgenerating portion is caused to generate heat with a required ignitingenergy to ignite and burn the priming.

[0122] By using such an igniter for an air bag system (or the integratedcircuit) , an amount of current (an amount of igniting energy) requiredfor activating the individual igniters normally is reduced, so that anamount of current (an amount of igniting energy) required for activatingthe entire igniters normally is also reduced. As a result, a capacitance(namely, a weight) of the capacitor for a backup power source can bemade small and the ECU itself can be made small. Accordingly, the weightof the entire air bag system can be reduced.

[0123] By igniting and burning the priming, the transfer charge in thegas generator in FIG. 2 or FIG. 3, and further the gas generating agentin the combustion chamber in FIG. 2, or the first gas generating agentin the first combustion chamber and the second gas generating agent inthe second combustion chamber in FIG. 3 are ignited and burnt togenerate a gas, and the gas is discharged from the gas dischargingports, thereby inflating an air bag accommodated in the module casetogether with the gas generator. In the gas generator in FIG. 3, theigniters 31 and 32 can be activated simultaneously or with a staggeredtime, or only the igniter 31 can be activated.

[0124] The air bag system is one shown in FIG. 1, it is provided withthe module case accommodating the gas generator for an airbag shown inFIG. 2 or FIG. 3 and the air bag, and it can be constituted to be thesame as the one specifically described on paragraphs 0096 to 0102 inJP-A 11-334517 and further, as the one shown in FIG. 17.

[0125] The igniter for an air bag system and the integrated circuit foran air bag system of the present invention can be applied as an igniterincorporated into various inflators (gas generators) such as an inflatorfor an air bag for a driver side, an inflator for an air bag for apassenger side next to the driver, an inflator for a side air bag, aninflator for a curtain air bag, an inflator for a knee-bolster air bag,an inflator for an inflatable seat belt, an inflator for a tubularsystem, and an inflator for a pretensioner, and an integrated circuitprovided in the igniter.

1. An igniter for an air bag system, which is one or at least twoigniters incorporated in the plural of the gas generators and used in anair bag system comprising an electronic control unit connected to apower source and an impact detecting sensor, and plural module caseswhich are connected to the electronic control unit and accommodateplural gas generators and plural air bags, wherein, in the air bagsystem, a bus line comprising plural loop wires which pass through theelectronic control unit is provided to supply and transmit currents andrequired information, and individual gas generators accommodated in theplural module cases are connected operationally by plural conductorsbranched at predetermined portions from the bus line, the one or atleast two igniters incorporated in the gas generator is each electricigniter which is provided with a heat generating portion and a primingcoming in contact with the heat generating portion to ignite the primingby heat generation of the heat generating portion due to an ignitioncurrent, and the igniter and the bus line are connected to each otherthrough plural conductors, and a capacitor and an integrated circuitrecorded with information for developing a required function areprovided in the igniter, a charging circuit for charging a current forigniting the priming in the capacitor is provided and a circuit forconverting an impedance of the charging circuit is provided between thebus circuit and the capacitor.
 2. The igniter for an air bag systemaccording to claim 1, wherein the capacitance of the capacitor is 250 pFto 24 μF.
 3. The igniter for an air bag system according to claim 1 or2, in which, among the currents from the bus circuit for charging thecapacitor and the required information, a rectifying circuit having afunction for rectifying an alternating current to make the current flowinto the capacitor as a direct current is further provided between thebus circuit and the capacitor, and the circuit for converting animpedance is provided in a path between the bus line and the rectifyingcircuit.
 4. The igniter for an air bag system according to claim 1 or 2,in which, among the currents from the bus circuit for charging thecapacitor and the required information, a rectifying circuit having afunction for rectifying an alternating current to make the current flowinto the capacitor as a direct current is further provided between thebus circuit and the capacitor, and the circuit for converting animpedance is provided between the rectifying circuit and the capacitor.5. The igniter for an air bag system according to claim 3 or 4, whereina function for amplifying at least one of the rectified voltage forcharging the capacitor and a voltage applied to the bus line exists. 6.The igniter for an air bag system according to any one of claims 1 to 5,wherein the impedance converting circuit is provided inside theintegrated circuit.
 7. The igniter for an air bag system according toany one of claims 1 to 6, wherein the impedance converting circuit isprovided with a function for controlling an upper limit of a currentvalue.
 8. The igniter for an air bag system according to any one ofclaims 1 to 7, wherein the integrated circuit has a circuit having afunction for detecting abnormality of the heat generating portion of theigniter in the gas generator, a circuit having a function foridentifying each of the plural gas generators and a circuit having afunction for detecting a malfunction of the capacitor.
 9. The igniterfor an air bag system according to any one of claims 1 to 8, in which acircuit for preventing the igniter from being activated erroneously by anoise generated outside of the igniter is further provided.
 10. Theigniter for an air bag system according to any one of claims 1 to 9, inwhich a discharging waveform converting circuit which converts a signalwaveform of a current for igniting an igniter stored in the capacitorfor each igniter is further provided.
 11. The igniter for an air bagsystem according to claim 10, wherein the discharging waveformconverting circuit exists in the integrated circuit.
 12. An integratedcircuit for an air bag system which is provided in one or at least twoigniters incorporated into the plural gas generators and used in an airbag system comprising an electronic control unit connected to a powersource and an impact detecting sensor, and plural module cases which areconnected to the electronic control unit and accommodate the plural gasgenerators and plural air bags, wherein in the air bag system, a busline comprising plural loop wires which pass through the electroniccontrol unit is provided to supply and transmit currents and requiredinformation, and individual gas generators accommodated in the pluralmodule cases are connected operationally by plural conductors branchedat predetermined portions from the bus line, the one or at least twoigniters incorporated in the gas generator is each electric igniterwhich is provided with a heat generating portion and a priming coming incontact with the heat generating portion to ignite the priming by heatgeneration of the heat generating portion due to an ignition current,and the igniter and the bus line are connected to each other throughplural conductors, and a capacitor and the integrated circuit areprovided in the igniter, and the integrated circuit is recorded withinformation for developing a required function, a charging circuit forstoring a current for igniting a priming in the capacitor is provided,and a circuit for converting an impedance of the charging circuit isfurther provided between the bus line and the capacitor.
 13. Theintegrated circuit for an air bas system according to claim 12, whereinthe capacitance of the capacitor is 250 pF to 24 μF.
 14. The integratedcircuit for an air bag system according to claim 12 or 13, in which,among the currents from the bus circuit for charging the capacitor andthe required information, a rectifying circuit having a function forrectifying an alternating current to make the current flow into thecapacitor as a direct current is further provided between the buscircuit and the capacitor, and the circuit for converting an impedanceis provided in a path between the bus line and the rectifying circuit.15. The integrated circuit for an air bag system according to claim 12or 13, in which, among the currents from the bus circuit for chargingthe capacitor and the required information, a rectifying circuit havinga function for rectifying an alternating current to make the currentflow into the capacitor as a direct current is further provided betweenthe bus circuit and the capacitor, and the circuit for converting animpedance is provided between the rectifying circuit and the capacitor.16. The integrated circuit for an air bag system according to claim 14or 15, wherein a function for amplifying at least one of the rectifiedvoltage for charging the capacitor and a voltage applied to the bus lineexists.
 17. The integrated circuit for an air bag system according toany one of claims 12 to 16, wherein the impedance converting circuit isprovided with a function for controlling an upper limit of a currentvalue.
 18. The integrated circuit for an air bag system according to anyone of claims 12 to 17, wherein the integrated circuit has a circuithaving a function for detecting abnormality of the heat generatingportion of the igniter in the gas generator, a circuit having a functionfor identifying each of the plural gas generators and a circuit having afunction for detecting a malfunction of the capacitor.
 19. Theintegrated circuit for an air bag system according to any one of claims12 to 18, in which a circuit for preventing the igniter from beingactivated erroneously by a noise generated outside of the igniter isfurther provided.
 20. The integrated circuit for an air bag systemaccording to any one of claims 12 to 19, in which a discharging waveformconverting circuit which converts a signal waveform of a current forigniting an igniter stored in the capacitor for each igniter is furtherprovided.
 21. The integrated circuit for an air bag system according toclaim 20, wherein the discharging waveform converting circuit exists inthe integrated circuit.
 22. A method for charging a capacitor providedin an igniter for an air bag system which is provided in one or at leasttwo igniters incorporated into the plural gas generators and used in anair bag system comprising an electronic control unit connected to apower source and an impact detecting sensor, and plural module caseswhich are connected to the electronic control unit and accommodate theplural gas generators and plural air bags, wherein in the air bagsystem, a bus line comprising plural loop wires which pass through theelectronic control unit is provided to supply and transmit currents andrequired information, and individual gas generators accommodated in theplural module cases are connected operationally by plural conductorsbranched at predetermined portions from the bus line, the one or atleast two igniters incorporated in the gas generator is each electricigniter which is provided with a heat generating portion and a primingcoming in contact with the heat generating portion to ignite the primingby heat generation of the heat generating portion due to an ignitioncurrent, and the igniter and the bus line are connected to each otherthrough plural conductors, and a capacitor, and a capacitor and anintegrated circuit recorded with information for developing a requiredfunction are provided in the igniter, a charging circuit for storing acurrent for igniting the priming in the capacitor is provided, and acircuit for converting an impedance of the charging circuit is providedbetween the bus circuit and the capacitor, and a current is suppliedfrom the power source via the bus line to charge the capacitor via thecircuit for converting an impedance.
 23. The method for charging acapacitor provided in an igniter for an air bag system according toclaim 22, wherein the capacitance of the capacitor is 250 pF to 24 μF.24. The method for charging a capacitor provided in an igniter for anair bag system according to claim 22 or 23, in which, among the currentsfrom the bus circuit for charging the capacitor and the requiredinformation, a rectifying circuit having a function for rectifying analternating current to make the current flow into the capacitor as adirect current is further provided between the bus circuit and thecapacitor, and the circuit for converting an impedance is provided in apath between the bus line and the rectifying circuit.
 25. The method forcharging a capacitor provided in an igniter for an air bag systemaccording to claim 22 or 23, in which, among the currents from the buscircuit for charging the capacitor and the required information, arectifying circuit having a function for rectifying an alternatingcurrent to make the current flow into the capacitor as a direct currentis further provided between the bus circuit and the capacitor, and thecircuit for converting an impedance is provided between the rectifyingcircuit and the capacitor.
 26. The method for charging a capacitorprovided in an igniter for an air bag system according to claim 24 or25, wherein a function for amplifying at least one of the rectifiedvoltage for charging the capacitor and a voltage applied to the bus lineexists.
 27. The method for charging a capacitor provided in an igniterfor an air bag system according to any one of claims 22 to 26, whereinthe impedance converting circuit is provided inside the integratedcircuit.
 28. The method for charging a capacitor provided in an igniterfor an air bag system according to any one of claims 22 to 27, whereinthe impedance converting circuit is provided with a function forcontrolling an upper limit of a current value.
 29. The method forcharging a capacitor provided in an igniter for an air bag systemaccording to any one of claims 22 to 28, wherein the integrated circuithas a circuit having a function for detecting abnormality of the heatgenerating portion of the igniter in the gas generator, a circuit havinga function for identifying each of the plural gas generators and acircuit having a function for detecting a malfunction of the capacitor.30. The method for charging a capacitor provided in an igniter for anair bag system according to any one of claims 22 to 29, in which acircuit for preventing the igniter from being activated erroneously by anoise generated outside of the igniter is further provided.
 31. Themethod for charging a capacitor provided in an igniter for an air bagsystem according to any one of claims 22 to 30, in which a dischargingwaveform converting circuit which converts a signal waveform of acurrent for igniting an igniter stored in the capacitor for each igniteris further provided.
 32. The method for charging a capacitor provided inan igniter for an air bag system according to claim 30, wherein thedischarging waveform converting circuit exists in the integratedcircuit.
 33. A gas generator for an air bag system comprising, in ahousing having a gas discharging port, an igniter activated by animpact, and one or at least two combustion chambers storing a gasgenerating agent ignited and burnt by the igniter to generate acombustion gas for inflating an air bag, wherein, as the igniter, anigniter for an air bag system according to any one of claims 1 to 11 isprovided.
 34. An air bag system comprising a gas generator for an airbag which comprises, in a housing having a gas discharging port, anigniter for an air bag system according to any one of claims 1 to 11activated by an impact and one or at least two combustion chambersstoring a gas generating agent ignited and burnt by the igniter togenerate a combustion gas for inflating an air bag, an impact sensorwhich senses an impact to activate the gas generator, an air bag whichintroduces a gas generated in the gas generator therein to inflate, anda module case which accommodates the air bag.